Image analysis was performed retrospectively by two chest radiologists (H.A. and Y.K.). The initial and the follow-up high-resolution CT scans were evaluated in random order without knowledge of the pathologic diagnosis, and the final assessment was achieved by consensus. The presence and location were determined for intralobular reticular opacity, septal line thickening, curvilinear subpleural opacity, ground-glass opacity, consolidation, traction bronchiectasis, and honeycombing. Curvilinear subpleural opacity was defined as linear opacity running parallel to the chest wall within 1 cm of the pleural surface. Ground-glass opacity was defined as areas showing a hazy increase of lung attenuation through which vessels could still be seen. Honeycombing was defined as end-stage lung damage, which was manifested as multiple thick-walled cysts. The anatomic distribution in the transverse section was described as being peripheral, central, peribronchial, or random. Peripheral predominance was noted if the abnormality was seen in the outer third of the transverse plane, and central predominance was noted if the abnormality was in the central third of the transverse plane. If abnormality was seen along the bronchovascular bundles, the distribution was regarded as peribronchial. If the abnormality had no predilection, it was regarded as randomly distributed. In the craniocaudal direction, the lung was evenly divided into three parts from the apex to below the right diaphragm, and these parts were denoted as the upper, middle, and lower zones. The extent of involvement of ground-glass opacity, reticular opacity (ie, intralobular reticular opacity and or septal line thickening), consolidation, honeycombing, and traction bronchiectasis was assessed independently for each of the three zones of each lung. The CT scan score in the upper, middle, and lower lung zones was determined by visually estimating the extent of each abnormality in each zone based on the percentage of the lung parenchyma that showed evidence of each abnormality in each zone (estimated to the nearest 5% of parenchymal involvement). The CT scan score was calculated by multiplying the percentage of each abnormality in each zone by a factor that corrected for differences in volume between the zones. The ratio of the volumes of the upper, middle, and lower lung zones was estimated as 1:1.6:1.3, based on previously published data.15
We also assessed the extent of the lung involved with any increased opacity (ie, reticular opacity, ground-glass opacity, or consolidation) in each zone of each lung and calculated the CT scan score in the same way. CT scan scores were compared between before and after treatments.